Methods for transferring a signal between semiconductor devices include an embedded method that includes embedding a clock in data. As illustrated in FIG. 9, in an embedded method, edges are recognized in a transmitted signal, and clock signals CLK1 and CLK1B are reproduced on the basis of the edges. The signal CLK1B is a signal with a phase having a phase lead angle of 180 degrees with respect to the signal CLK1.
In one of embedded methods which uses both of an up-edge and a down-edge of a clock as triggers for data, clock signals CLK2 and CLK2B having phase lead angles of 90 degrees are generated from reproduced clock signals CLK1 and CLK1B, and data is taken in from a transmitted signal by using the clock signals. The signal CLK2B is a signal having a phase lead angle of 180 degrees with respect to the signal CLK2. For this reason, data can be taken in at the center of a signal period which has a lead angle of 90 degrees with respect to an edge. That is, in this case, the first half of an up or down period of a signal is a setup period while the second half of an up or down period of the signal is a hold period.
There is known a process of a variable 45 degrees phase-shift circuit of receiving a feedback signal and changing a characteristic value of the circuit, thereby adjusting a phase lead angle to 0 degrees and an angle of phase difference to 45 degrees.
There is also known a process of inputting, transforming, and outputting a differential clock signal whose phase with data is adjusted and feeding back a signal generated on the basis of the differential clock signal to control an amount of transformation for a differential clock signal.